In the welding industry, the need for accelerating welding speed and reducing the amount of spatters has intensified in recent years. The accelerated welding speed leads to increase in the volume of production in a fixed time. Similarly, the suppressed spatters eliminate the post-welding process for removing spatters from a work, thereby increasing productivity of welding.
Pulse welding output control has conventionally begun with the start of the output of pulse current. When an arc is properly provided with no short-circuit between a wire and a base metal after a predetermined second period that is shorter than a first period as a basic pulse interval, a pulse welding output controller feeds a successive pulse current according to the basic pulse interval.
On the other hand, when a short circuit occurs between the wire and the base material after the second period, the controller feeds a current having a speed lower than a pulse-rising speed of pulse current. When the short circuit between the wire and the base material is recovered, the controller feeds a current so as to be smaller than a pulse current and to be larger than a base current for a predetermined period. After that, the controller feeds the next pulse current. Suggestions on reducing spatters in welding have been made, and one of which is introduced in, for example, Japanese Patent Unexamined Publication No. H01-266966.
Hereinafter will be described a pulse welding control in a conventional pulse arc welding device with reference to FIG. 4. FIG. 4 shows a current waveform in a conventional output control in a conventional pulse arc welding device. FIG. 4 shows time in the horizontal direction and shows welding current in the vertical direction. FIG. 4 also shows first pulse intervals 101-1 and 101-2; short-circuit period 102 during which a short-circuited condition is maintained between a wire and a base material; and arc initial time (period) 103 for preparing a melted nugget for forming droplets after the short circuit is recovered.
At time 106—the end of basic pulse interval 101-2, the wire and the base material maintain a short-circuited condition. During short-circuit period 102 including time 106, a welding current controller maintains a short-circuit control. After the short circuit is recovered, the controller feeds arc current 105L—lower than peak current 105, and arc current 104H—higher than base current 104—in arc initial period 103 to prepare a melted nugget for forming droplets for next welding. After a lapse of arc initial period 103, the controller applies pulse current. Through the control above, spatters have been decreased.
To be more specific, according to a conventional pulse arc welding device, when a short circuit occurs, the output controller of the device carries out with a higher priority the short-circuit control by a dip-waveform circuit section (not shown), meanwhile the pulse control by a pulse-waveform circuit section is put into a standby mode. In this way, spatters have been reduced.
Such an output control of a conventional pulse arc welding device, however, has pending problems. For example, seeking for more accelerated welding speed (e.g., higher than 1.5 m/min.), with a high welding current (e.g., 250-350 A) maintained, causes undercut and humping. To avoid these inconveniencies, lower welding voltage is required. The lower setting of welding voltage not only prolongs the short-circuit period (from the occurrence of a short circuit until the short circuit is recovered), but also increases the amount of current supplied when the short circuit is recovered. The higher the welding current (for example, set at 300 amperes), the shorter the base period. Such a prolonged short-circuit period in the high current region of the basic pulse interval causes delay in pulse-starting time for the next pulse. This prevents a wire fed according to a defined welding current from having a proper melt, resulting in unstable arc condition.